were observed for about one year, especially at the critical and recovery stages. A slight increase of "mitotically connected abnormalities" was found in bone marrow smears of a few cases after 10 years. cytes, f. Recovery: erythrocytes, The cumulative distribution curves of numbers of leuko- and platelets were notably displaced to the left of nor- mal at the critical stage. Though the curves of erythrocytes and platelets were the same as in normal Japanese people after 2 years, the curve of leukocytes was still displaced slightly to the left of normal even after 6 years. 4. Cytogenetics Follow-up of chromosome observations in blood cells has been performed since 1964. Even 25 years after exposure, cells with chromosome abnormalities (both dicentric and ring and Cs cells) are found in the peripheral lymphocytes with much higher frequencies than in normal Japanese people 40 to 50 years of age. The frequency of dicentric and ring forms seems to be decreasing, but Cs cells remained fairly constant at a frequency of 2 to 3%. The frequencies of the chromosome abnormalities in the 1969 examination were found to correspond to the severity of injuries indicated by minimum leukocyte counts at the critical stage. In the bone marrow, cells with chromosome abnormalities (Cs cells) occurred rather consistently with frequencies of >2% at all four times of sampling carried out 13 to 17 years after exposure. 5. Spermatopoiesis The number of spermatozoa decreased about 2 months after exposure, and azoospermia was found. Both reduced motility and morphological abnormalities of spermatozoa were also observed. Indications of recovery were noted about 2 years after exposure. Since then most of the patients have had healthy children. The testicle of the fatal case, who died 206 days after exposure, showed extremely reduced spermatopoiesis. 6. Other Findings Disturbances of the liver function were found to a slight degree in a few cases at the time of hospitalization. Later these became more obvious. One of the fishermen who showed remarkable hematological disturbances died from liver damage. During follow-up studies, elevated values of GOT and GPT were observed in several cases. In 1974 ascites developed in two cases, and in one it was accompanied by diabetes mellitus and sepsis. Although both cases recovered, they died of liver cirrhosis in 1974 and 1979 respectively. Ophthalmological examinations showed slight lenticular opacities in several cases. However, these had no characteristics of radiation-induced cataracts as observed in A-bomb survivors. Other studies, including thyroid studies, are continuing in order to detect late effects of radiation. ~ 138 -